Folding knives of the type wherein the blade is pivotable between an open position wherein the cutting edge of the blade is exposed and a closed position wherein the cutting edge of the blade is received in a recess in the handle are well known. Also well known are various safety features for securing the blade against accidental opening or closing for preventing injury.
One such arrangement is disclosed in U.S. Pat. No. 4,240,201 issued to Sawby et al. In Sawby, the top of the blade receiving recess is defined by a bar spring secured at its rear end such that the front end is free for limited upward movement. A projection at the front end of the bar spring seats in a complementary notch in the blade tang for positively securing the blade in its open position. To pivot the blade from the open to the closed position, Sawby provides a push button mechanism extending through the handle and into the recess, the mechanism having a camming surface which mates with a corresponding camming surface on the bar spring whereby depression of the push button cams the bar spring upward thereby unseating the projection from the notch whereupon the blade may be moved to its closed position. In the closed position, the front end of the bar spring abuts a surface of the tang opposite the notch. However, there is no positive engagement between the bar spring and the tang in this position. Consequently, the knife may be moved from the closed position to the open position without depressing the push button as rotation of the blade will inherently urge the bar spring upward to accommodate such movement.
In addition to the absence of any positive locking of the blade in the closed position, which is desirable as where the blade is unintentionally acquired by a child, the cooperation of the projection on the bar spring and the notch in the blade tang for securing the blade in the open position is subject to failure as the parts wear over a period of time.